这个sql咋写？
这个sql咋写？
两个表的结构一模一样，数据大部分是重复，小部分不同；
要求：
1.如果a列数据相同，计算b列相减的结果
test1:
a b
xxx 1
yyy 2
zzz 3
test2：
a b
xxx 3
zzz 2
qqq 1
查询结果结果为：
a b
xxx 2
zzz -1
yyy -2
qqq 1
Create Table:
CREATE TABLE test1(a VARCHAR2(20),b NUMBER);
CREATE TABLE test2(a VARCHAR2(20),b NUMBER);
INSERT INTO test1 VALUES('xxx',1);
INSERT INTO test1 VALUES('yyy',2);
INSERT INTO test1 VALUES('zzz',3);
INSERT INTO test2 VALUES('xxx',3);
INSERT INTO test2 VALUES('zzz',2);
INSERT INTO test2 VALUES('qqq',1);
SELECT * FROM test1;
SELECT * FROM test2;
Solution 1:
SELECT a
,SUM(c) AS b
FROM (SELECT a
,-1 * b AS c
FROM test1
UNION ALL
SELECT a
,b AS c
FROM test2)
GROUP BY a;
A B
-------------------- ----------
yyy -2
zzz -1
xxx 2
qqq 1
Solution 2:
SELECT nvl(t2.a, t1.a) a
,(nvl(t2.b, 0) - nvl(t1.b, 0)) b
FROM test2 t2
FULL OUTER JOIN test1 t1 ON (t2.a = t1.a);
A B
-------------------- ----------
xxx 2
yyy -2
zzz -1
qqq 1
来自：CU-ORALCE群
JOIN复习:
SQL> SELECT nvl(t2.a, t1.a) a
2 ,(nvl(t2.b, 0) - nvl(t1.b, 0)) b
3 FROM test2 t2
4 RIGHT JOIN test1 t1 ON (t2.a = t1.a);
A B
-------------------- ----------
xxx 2
zzz -1
yyy -2
SQL>
SQL> SELECT nvl(t2.a, t1.a) a
2 ,(nvl(t2.b, 0) - nvl(t1.b, 0)) b
3 FROM test2 t2,test1 t1
4 WHERE t2.a(+) = t1.a;
A B
-------------------- ----------
xxx 2
zzz -1
yyy -2
SQL> SELECT nvl(t2.a, t1.a) a 2 ,(nvl(t2.b, 0) - nvl(t1.b, 0)) b 3 FROM test2 t2 4 LEFT JOIN test1 t1 ON (t2.a = t1.a); A B -------------------- ---------- xxx 2 zzz -1 qqq 1 SQL> SQL> SELECT nvl(t2.a, t1.a) a 2 ,(nvl(t2.b, 0) - nvl(t1.b, 0)) b 3 FROM test2 t2,test1 t1 4 WHERE t2.a = t1.a(+); A B -------------------- ---------- xxx 2 zzz -1 qqq 1
原文链接： http://blog.csdn.net/t0nsha/article/details/6394037